The reducers of power units are being studied. Dynamic analysis of the basic structural elements of reducers has been carried out. There have been found the possible causes of the increased wear of surfaces of toothed linkages of herringbone transfer. There are given the results of studying dynamic interactions by vibration characteristics of measuring the vibration level in bearing blocks and elements of reducers of power units at their technological operation mode. To analyze the frequency interaction of structural elements of the studied reducers there were used the results of modal analysis of earlier conducted researches of the reducer power unit. It has been stated that for conducting vibrodiagnostic control the third class machines were chosen due to their powerful primary engines, and other machines with rotating masses mounted on massive foundations, rigid in the direction of vibration measurement. Phase angles of high-speed and low-speed shaft wheels for the purpose of defining a corner of phase shift (torsional fluctuations of shaft wheels) at reverse frequencies and frequencies of toothed linkage have been studied. In terms of dynamic analysis it allows to trace trajectories of linkages in toothed couples of divided wheels of herringbone gearing. The diagrams of gear trajectories are illustrated for bending vibrations of the shaft-wheels. The research results confirming the nonlinear relationship between the level of axial vibrations and the displacement angle of instantaneous phase angle are presented. It has been recommended to reduce the level of axial vibration transmitted from the coupling to 0.1–0.2 mm/s for eliminating uneven wear in the chevron gear; carry out structural improvements to the high-speed and low-speed shaft-wheels with increasing rigidity between the elements of chevron transmission; operate gearboxes within critical values; timely monitor the technical condition of gearboxes.